A wireless local area network (WLAN) in Infrastructure basic service set (BSS) mode has an Access Point (AP) for the BSS and one or more stations (STAs) associated with the AP. The AP typically has access or interface to a distribution system (DS) or another type of wired/wireless network that carries traffic into and out of the BSS. Traffic to STAs that originates from outside the BSS arrives through the AP and is delivered to the STAs. Traffic originating from STAs to destinations outside the BSS is sent to the AP to be delivered to the respective destinations. Traffic between STAs within the BSS may also be sent through the AP where the source STA sends traffic to the AP and the AP delivers the traffic to the destination STA. Such traffic between STAs within a BSS is really peer-to-peer traffic. Such peer-to-peer traffic may also be sent directly between the source and destination STAs with a direct link setup (DLS) using an 802.11e DLS or an 802.11z tunneled DLS (TDLS). A WLAN in Independent BSS mode has no AP and STAs communicate directly with each other.
New spectrum is being allocated in various countries around the world for wireless communication systems such as WLANs. Such spectrum is often limited in the size and bandwidth of the channels they comprise. In addition, the spectrum may be fragmented in that available channels may not be adjacent and may not be combined for larger bandwidth transmissions. Such is the case, for example, in spectrum allocated below 1 GHz in various countries. WLAN systems, for example built on the 802.11 standard, may be designed to operate in such spectrum. Given these limitations, the WLAN systems will only be able to support smaller bandwidths and lower data rates compared to high throughput (HT)/very high throughput (VHT) WLAN systems, for example, based on the 802.11n/802.11ac standards.
The IEEE 802.11ah Task Group (TG) has been established to develop solutions to support WLAN systems in the sub-1 GHz band and to achieve the following requirements: orthogonal frequency division multiplexing (OFDM) physical (PHY) layer operating below 1 GHz in license-exempt bands excluding television white space (TVWS); enhancements to the medium access control (MAC) layer to support the PHY and coexistence with other systems; and optimization of rate versus range performance (range up to 1 km (outdoor) and data rates greater than 100 Kbit/s).
The following use cases have been adopted: sensors and meters; backhaul sensor and meter data; and extended range WiFi for cellular offloading. The spectrum allocation in some countries is limited. Therefore, there is a need to support a 1 MHz only option in addition to support for a 2 MHz option with a 1 MHz mode. The 802.11ah PHY is required to support 1, 2, 4, 8, and 16 MHz bandwidths.
The 802.11ah PHY operates below 1 GHz and is based on the 802.11ac PHY. To accommodate the narrow bandwidths required by 802.11ah, the 802.11ac PHY is down-clocked by a factor of 10. While support for 2, 4, 8, and 16 MHz bandwidths may be achieved by the 1/10 down-clocking support for the 1 MHz bandwidth requires a new PHY definition with a Fast Fourier Transform (FFT) size of 32.
In the sensors and meters use case, up to 6000 STAs are supported within one BSS. The devices such as smart meters and sensors have different requirements pertaining to the supported uplink and downlink traffic. For example, sensors and meters may be configured to periodically upload their data to a server which will most likely to be uplink traffic only. Sensors and meters may also be queried or configured by the server. When the server queries or configures a sensor or meter, it will expect that the queried data should arrive within a setup interval. Similarly, the server/application will expect a confirmation for any configuration performed within a certain interval. These types of traffic patterns are different than the traditional traffic patterns assumed for WLAN systems.
In the signal (SIG) field of the physical layer convergence procedure (PLCP) preamble of a packet, two bits are used to indicate the type of acknowledgment (ACK) expected as a response (i.e., early ACK indication) to the packet: ACK (“00” value), block ACK (BA) (“01” value), no ACK (“10” value), and that a packet will be transmitted in the following frame (“11” value).
High Efficiency WLAN (HEW) is directed to enhancing the Quality of Experience (QoE) for a broad spectrum of wireless users in many usage scenarios, including high-density scenarios in the 2.4 GHz and 5 GHz bands. New use cases which support dense deployments of APs and STAs, and associated Radio Resource Management (RRM) technologies are being considered. Potential applications for HEW include usage scenarios such as: data delivery for stadium events, high user density scenarios such as train stations or enterprise/retail environments, an increased dependence on video delivery, and wireless services for medical applications.